The present invention relates in general to an exhaust gas recirculation system in an internal combustion engine, particularly in a self-ignition type IC engine.
From U.S. Pat. No. 4,177,777 an exhaust gas recirculation control system is known in which the amount of air fed into the internal combustion engine is measured by an air flow sensor and, together with additional possible operational parameters, the measured value is converted into a control signal which varies the control pressure for a pneumatically operated exhaust gas return valve so as to adjust the amount of the recirculating gas. In addition, U.S. Pat. No. 4,177,777 discloses an exhaust gas recirculating system which measures the amount of recirculated exhaust gas and compares the measured value with a desired value generated from the measured volumetric flow rate. The resulting correction signal is used for adjusting the position of the exhaust gas recirculation valve. The first-mentioned step has the disadvantage that the amount of recirculating exhaust gas is controlled without taking into account possible interferences. The second solution requires a measuring arrangement for the actual amount of the recirculating exhaust gas and problems encountered in this solution are sufficiently known. They arise particularly from high temperature of the exhaust gas as well as from the contents of solid particles which make the long-term stability of the exhaust gas measurement extremely problematic.
Similar prior art exhaust gas recirculation systems are known also from U.S. Pat. Nos. 4,164,032, 4,164,206, 4,142,493, 4,173,203, 4,161,929, 4,250,706 and from the German publication DE-OS No. 2,851,180.